This application claims priority of German Application No. 199 40 095.4, filed Aug. 24, 1999 and International Application No. PCT/EP00/07616, filed Aug. 5, 2000, the complete disclosure of which is hereby incorporated by reference.
1. a) Field of the Invention
In the field of graphite furnace atomic absorption spectroscopy (GF-AAS analysis), tubular furnace bodies and atomizing furnaces based on graphite and Zeeman magnetic field arrangements for compensation of unwanted measurement signals are state of the art. In this connection, extensive descriptions are contained in DE 4243766 C2, DE 4243767 C2, EP 0364539 B1, EP 0363457 and DE 2165106 C2.
2. b) Description of the Prior Art
Generally, a distinction is made between longitudinally heated furnace bodies and transversely heated furnace bodies, wherein separate specimen carriers or platforms, as they are called, or specimen carriers which are connected with the furnace body can be provided in the interior of the respective furnace part. The geometry in the transversely heated furnace bodies has clear analytic and economic advantages over the longitudinally heated type.
For dissolved (liquid) and solid specimens, it is state of the art in GF-AAS analysis to use separate atomizing devices associated with and adapted to the shape and type of specimen and containing either a transversely heated or a longitudinally heated furnace body. Consequently, for example, a laboratory having to analyze both forms or types of specimen must be equipped with two different complete systems of atomic absorption spectrometers, including the accessory units, e.g., peripheral equipment for the specimens.
Typically, the specimens are introduced into the center of the interior space of the furnace body by means of automatic feeders, also known as specimen feeders. In the case of dissolved specimens, the furnace bodies are charged vertically or diagonally from the top.
Solid specimens, on the other hand, are initially deposited outside the furnace on a spoon-like graphite specimen carrier and are quantified by determining the weight of the specimen. The specimen carrier with the specimen is then inserted into the atomizing device approximately horizontally via side openings.
Further, it is conventional in GF-AAS analysis to utilize the Zeeman effect, as it is called, for background compensation. Systems using a procedure of this type are known, for example, from EP 0364539 B1, EP 0363457 B1 and DE 2165106 C2.
EP 036357 B1 and DE 2165106 C2 disclose atomic absorption spectrometers in which a furnace through which a measurement light bundle is radiated is arranged in the air gap of an electromagnet for generating the Zeeman effect.
In this connection, DE 21655106 C2 discloses a GF-AAS atomizing device with Zeeman magnets which are arranged transversely relative to the furnace tube axis, wherein it is not possible to use transversely heated furnace bodies.
It is disadvantageous that the closed, transversely heated construction of the atomizing device and the magnetic poles described in EP 036357 B1 do not permit horizontal feeding of solid specimens, but only permit dissolved specimens to be inserted vertically from above via a fill opening. On the one hand, the longitudinally arranged, bulky magnetic poles must be moved up very close to the front end faces of the furnace tube in order to realize the maximum magnetic field strength of approximately 1 Tesla needed for analysis; on the other hand, however, because of this very circumstance, the field of use for transversely heated furnace tubes, which are so advantageous in terms of analysis, in combination with a longitudinal magnetic field arrangement, is limited only to dissolved specimens.
It is the primary object of the invention to provide an atomizing device for an atomic absorption spectrometer which is outfitted with transversely heated furnace bodies and with an electromagnet for background correction using the Zeeman effect and which is accordingly equally suited to the analysis of solid and dissolved specimens.
This object is met by an atomizing device for atomic absorption spectroscopy according to the Zeeman method, wherein a tubular atomizing furnace which is transversely heated via wings and with horizontally oriented furnace tube is located with its furnace wings between vertically arranged electrodes for examination of liquid specimens fed from the top and for examination of solid specimens fed from the side.
According to the invention, an atomizing device for dissolved specimens as well as solid specimens is realized in that a transversely heated furnace tube is arranged in vertically disposed electrodes by means of its contact pieces and the contact pieces of the furnace are provided with centrally supported bore holes for introducing dissolved specimens, for supplying and discharging protective gases, and for detecting tube radiation for purposes of controlling the temperature of the furnace.
Due to this vertical placement of the transversely heated furnace, it is possible, first, to provide the necessary free space for the magnetic poles of a transversely oriented Zeeman magnetic field arrangement which are to be moved up close to the furnace and, second, the front areas of the tubular part of the furnace are kept free such that a horizontal insertion opening for solid specimens which can also be closed periodically by an optical window can be formed on one side, preferably on the left-hand front side of the furnace.
Another step, according to the invention, for providing the necessary free space for insertion of solid specimens is the asymmetric arrangement of the geometric centers of the furnace and magnetic poles relative to one another.
Further, according to the invention, the fill openings for dissolved and solid specimens are outfitted in a simple manner with exchangeable graphite adapters. In this way, quick geometric adaptation to the respective specimen feeders in use can be carried out and the duct not in use can be closed quickly on the one hand and, on the other hand, a possibility is provided for simple cleaning without completely disassembling the atomizing device.
In particular, the inventive solution has the advantages of the Massman furnace technique with Zeeman magnetic field for solid and dissolved specimens which essentially comprise a half-closed atomizer with two tubular furnace parts adapted to the possible specimen forms and separate outer and inner protective gas flows. Also, the exchangeable graphite partsxe2x80x94two for the furnace tube and three for duct adaptersxe2x80x94which are adapted to the specimen form are designed as graphite closing parts which can be produced inexpensively and exchanged in a simple manner.